1. Field of the Invention
The present invention relates to a monitoring diagnostic apparatus for monitoring abnormalities or determining/predicting causes of abnormalities of electrical equipment such as circuit breakers, switches, disconnecting switches, voltage transformers, current transformers, general transformers, bus bars, insulation meters, generators, rotary machines, oil-insulated electrical equipment, air-insulated electrical equipment, vacuum-insulated electrical equipment and solid-insulated electrical equipment.
2. Description of the Prior Art
FIG. 17 is a diagram showing the configuration of a monitoring diagnostic apparatus adopting a technique described in a report with the title "Development of Preventive Maintenance System for Highly Reliable Gas-Insulated Switchgear" with reference to FIG. 4 on page 4 of Power Engineering Society presented in an IEEE winter meeting in 1990.
Reference numeral 1 shown in FIG. 17 is electrical equipment such as a spacer of a circuit breaker whereas reference numeral 2 denotes a tank of the circuit breaker 1. Reference numerals 3 and 4 are a central conductor of the circuit breaker 1 and a transmission line to the circuit breaker 1, respectively. Reference numeral 5 is a foreign substance sticking to the central conductor 3 whereas reference numeral 6 denotes a partial-discharge phenomenon caused by the foreign substance 5. Reference numerals 7 and 74 are an acceleration sensor attached to the tank 2 and an ultrasonic sensor, respectively. Reference numeral 75 denotes a processor for dividing an output A of the acceleration sensor 7 by an output B of the ultrasonic sensor 74 to give a result C. Reference numeral 76 is a comparator for determining whether or not the result C is greater than a predetermined threshold value Th. The processor 75 and the comparator 76 constitutes a controller denoted by reference numeral 77 for implementing a monitoring diagnostic algorithm. Reference notation D is a monitor diagnostic result.
Next, the principle of operation of the monitoring diagnostic apparatus is described. First of all, the processor 75 computes the value C (=A/B) as a ratio of the output A of the acceleration sensor 7 to the output B of the ultrasonic sensor 74. The value of the ratio C is then supplied to the comparator 76 to be compared to the threshold value Th. A ratio value C greater than the threshold value Th is regarded as a symptom of an abnormality occurring in the circuit breaker 1. A ratio value C smaller than the threshold value Th, on the other hand, is regarded as a noise. It should be noted that the threshold value Th is determined in advance by experiments or from previous experiences.
In the conventional monitoring diagnostic apparatus described above, an algorithm is adopted for detecting an abnormality. According to the algorithm, the value C, a ratio of outputs of two kinds of sensors, is compared to the threshold value Th. A ratio value C greater than the threshold value Th is regarded as a symptom of an abnormality. It is thus necessary to determine in advance the threshold value Th by experiments or from previous experiences. In addition, the conventional monitoring diagnostic apparatus cannot adapt itself to changes in case of the circuit breaker, various kinds of noise differing from installation site to installation site or changes with the lapse of time.
Moreover, two kinds of sensors are employed. The sensors give rise to a problem that in some cases only one sensor can be installed. If three or more sensors are used, the range of applications becomes even narrower because the conventional monitoring diagnostic apparatus cannot make use of information output by the additional sensors. In addition, the conventional monitoring diagnostic apparatus has a problem that the conventional algorithm employed therein provides only information on whether the electrical equipment is normal or abnormal. The cause of a detected abnormality cannot thereby be identified.